Since the advent of mechanized transportation by way of wheeled vehicles, the desirability of incorporating a braking mechanism into such a vehicle has been recognized. Such braking assemblies are necessary to control the speed of the vehicle as well as to bring it to a stop at a desired location. The typical brake for such a vehicle utilizes a braking member which is brought into contact with either the wheel itself or a mechanical element which rotates in conjunction with the wheel so that a frictional force applied by the braking element acts to retard and then stop the wheel rotation. Among the various braking mechanisms known, motorized vehicles of today's manufacturers typically employ either drum brakes, disk brakes or a combination of the two.
As is well known, a drum brake incorporates a plurality of arcuate brake shoes mounted inside a wheel drum which supports a wheel or tire. Upon activation, the brake shoes move radially outwardly to contact the inner arcuate surface of the drum and thereby apply a braking force. On the other hand, disk brakes employ a disk-shaped element which rotates rigidly with respect to the wheel. Here, a caliper mechanism straddles the edge of the disk, and a pair of opposed brake pads are positioned between the ends of the caliper structure so that, upon actuation, the brake pads are advanced towards one another thereby trapping the disk between their braking surfaces thereby applying the braking force. In either event, the brake pads or brake shoes employ brake pad elements that are typically constructed of a hard non-lubricous composite.
Many pedal powered cycle vehicles, such as bicycles, tricycles and the like, employ the caliper brake concept but utilize a different mechanical structure since typically the work necessary to bring the vehicle to a stop is less for a pedal powered vehicle than a motorized vehicle due to the reduced mass in motion. These brakes include those known both as "caliper" brakes and "cantilever" brakes. In either event, the caliper brake assembly for pedal powered vehicles typically employs a pair of brake arms that are pivoted to the frame of the cycle vehicle and terminate in free ends on either side of the rim of the cycle's wheel. Brake shoes are mounted in opposed, facing relationship to one another on either side of the wheel rim. The operator employs a hand brake lever to reciprocate a wire inside a cable with this wire connected to the brake arms so as to pivotally advance the free ends toward and away from the wheel rim so that the brake shoes may be placed in a braking state wherein the brake shoe engages the moving wheel rim and in a brake release state wherein the brake shoe is disengaged from the wheel rim.
While bicycle brakes are currently undergoing revolutionary changes in design, materials and usage, brake shoes and their brake pads have remained remarkably unchanged. For a number of decades these brake shoes have utilized a brake pad constructed of carbon-infused rubber which is thought to have a high coefficient of friction and thus a good material for such a brake pad. Even though cyclists are today riding more aggressively and demanding more control of their cycle vehicles through higher performance of the cycle components, little has been done to improve brake pad performance. Such innovation has been directed to varying tread designs for the brake pad body.
While rubber brake shoes have been relatively effective in their application of braking force to a bicycle wheel, there remains many problems associated with such structures. Where these brake pads have a high coefficient of friction, they are typically subject to increased sliding abrasion so that, for cyclists who ride frequently or aggressively, especially over rugged terrain, brake shoes will typically wear out in a short period of time, often within one week. Moreover, the wear of brake shoes during braking events deposits brake material on the wheel rim. This deposit often hardens into a glaze which may make braking less efficient; this glaze is often difficult to remove. Likewise, the surface of the brake shoe is also subjected to such glazing which is similarly difficult to remove.
The use of such rubber brake pads can also cause damage to the bicycle wheel. On one hand, worn brake shoes often expose parts of their metal support structures, and contact of the metal support structure on the metal rim can cause extensive damage. Rubber brake pads may become embedded with small slivers of aluminum from the wheel rim; when applied, the brake pads then further score the rim.
A significant disadvantage of rubber brake shoes appears when the cycle is ridden in wet or raining conditions. When such conditions exist, moisture collects on the wheel rim and such moisture greatly reduces the coefficient of friction between the brake pad and the wheel rim to such a degree that it is not uncommon for accidents and injury to result due to the inability of the cyclist to brake effectively when confronted with hazards. This is exacerbated by the presence of abraded rubber particles and dust deposited on the rim since such particles may become suspended in the moisture, thus forming a lubricous film.
As noted above and despite the disadvantages mentioned, there has been little done to improve brake pads. Thus, there has been a long felt need for such improvements in pad material, construction and the methods of manufacturing the same.
The present invention attempts to meet this need by providing a brake shoe incorporating a urethane-based brake pad that has high tensile and compression properties and which exhibits superior braking performance, especially in wet conditions. While this brake shoe is especially constructed for use with caliper-type brakes for bicycles and other cycle vehicles, the advantages provided by this brake shoe could be employed, as desired, in other mechanized vehicle applications.